Electricity: measuring and testing – Impedance – admittance or other quantities representative of...
Reexamination Certificate
2000-04-26
2003-12-02
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
C324S691000, C324S693000, C324S750010
Reexamination Certificate
active
06657439
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sheet resistance meter for measuring a sheet resistance of a thin-film metal or alloy formed on a substrate, for example, a semiconductor wafer, with a sputtering or vapor deposition technique.
BACKGROUND OF THE INVENTION
Conventionally, film properties, such as thickness, composition, and size, of a thin-film metal or alloy formed on a glass substrate by a sputtering or vapor deposition technique (hereinafter, will be referred to simply as a thin-film metal) are evaluated by means of measurement of a sheet resistance of the thin-film metal. That is, the properties of a thin-film metal formed on a glass substrate are evaluated according to whether or not the sheet resistance measured falls within a predetermined range or stays below a reference value.
For this purpose, the sheet resistance may be measured, for example, through a sensor section directly contacting the thin-film metal (contact-type sheet resistance measurement technique). An example of the contact-type sheet resistance measurement technique is a four-probe scheme.
The following description will explain the evaluation of properties of a thin-film metal by a four-probe scheme in reference to FIG.
28
. Note that in the four-probe scheme, the sheet resistance is not directly measured for evaluation of the properties the thin-film metal. Instead, the resistivity of the thin-film metal is measured, and the sheet resistance is obtained based on the resistivity.
First, four needle-like electrodes (probes)
203
, arranged in a straight line, are placed on a thin-film metal
202
formed on a substrate
201
, and a current I is applied to the two outer probes
203
to measure the potential difference V developing between the two inner probes
203
and eventually obtain the resistance (R=V/I).
Subsequently, the obtained resistance R is multiplied by the thickness t of the thin-film metal
202
and a dimensionless correction factor F determined from the shape and dimensions of the thin-film metal
202
as well as from the position of the probes
203
, so as to obtain the resistivity &rgr; of the thin-film metal
202
. The sheet resistance is obtained based on the resistivity &rgr;.
In the four-probe scheme, the probes
203
are brought into contact with the thin-film metal
202
to measure the resistivity &rgr;; the thin-film metal
202
may be scratched and cause fine dust, and the probes
203
may wear out and need be changed regularly.
Further, measurement cannot be performed if the object, i.e., the thin-film metal
202
on the substrate
201
, is shaking. Therefore, a dedicated attach stage needs be provided on which the substrate
201
is firmly attached. The resistivity measuring device containing such a dedicated attach stage would be inevitably bulky; therefore its accommodation in an existent manufacturing line of the thin-film metal
202
on the substrate
201
is difficult, let alone in-line measurement of the resistivity &rgr; of the thin-film metal
202
.
Another method suggested to evaluate properties of a thin-film metal is a non-contact method (non-contact-type sheet resistance measurement technique) whereby the sheet resistance of a thin-film metal is measured through metal needles or the like that do not contact the thin-film metal.
According to the non-contact-type sheet resistance measurement technique, the sheet resistance of the thin-film metal is measured by means of the eddy currents that are induced in the thin-film metal by application of high frequency electric power and lost as Joule heat.
In other words, the non-contact-type sheet resistance measurement technique makes use of the positive correlation between the conductivity and the dissipation of high frequency electric power in a thin-film metal, so as to obtain the conductivity (the reciprocal of resistivity) of a thin-film metal on a semiconductor wafer in a non-contact manner. Note that in the non-contact-type sheet resistance measurement technique, the sheet resistance of the thin-film metal is not directly measured for evaluation of the properties of the thin-film metal. Instead, the conductivity of the thin-film metal is measured, and the sheet resistance is obtained based on the conductivity.
Specifically, as shown in
FIG. 29
, a semiconductor wafer
301
on which a thin-film metal is formed is placed in the gap (measurement distance: 1 to 2 mm) of a ferrite core
302
around which a coil
303
connected to a high frequency generation circuit
304
is wound. Eddy currents are induced in a thin-film metal on the semiconductor wafer
301
. The induced eddy currents are lost as Joule heat, and therefore the high frequency electric power is dissipated in the thin-film metal on the semiconductor wafer
301
.
Hence, the high frequency electric power dissipated in the thin-film metal on the semiconductor wafer
301
is detectable as eddy current loss. The eddy current loss is transferred from the coil
303
via the high frequency generation circuit
304
to the wave detection circuit
305
and supplied as a difference in the output voltage. Then, the control circuit (not shown) obtains the conductivity of the thin-film metal on the semiconductor wafer
301
based on the output voltage from the wave detection circuit
305
. Then the sheet resistance is obtained from the conductivity.
In the non-contact-type sheet resistance measurement technique, there is no sensor section directly in contact with the object, i.e., the thin-film metal: therefore, unlike in the contact-type sheet resistance measurement technique, the thin-film metal is not scratched nor does not cause fine dust, and no probes are involved that may wear out and need be changed regularly.
Incidentally, in view of control of product quality of semiconductor wafers and other glass substrates on which a thin-film metal is formed, it is preferable to measure the sheet resistance for every semiconductor wafer, etc. manufactured. To realize this, the sheet resistance should be measured for every semiconductor wafer in-line, i.e., without the semiconductor wafer leaving the manufacturing line.
In the foregoing non-contact-type sheet resistance measurement technique, as shown in
FIG. 29
, the ferrite core
302
is shaped so as to clamp the semiconductor wafer
301
to induce eddy currents in the thin-film metal on the semiconductor wafer
301
.
Therefore, the structure of the ferrite core
302
shown in
FIG. 29
renders it difficult to measure the sheet resistance on an existent manufacturing line; in order to measure the sheet resistance of the thin-film metal on a semiconductor wafer, the semiconductor wafer needs be removed from the manufacturing line to measure the sheet resistance at a different place.
Therefore, it is time-consuming to measure the sheet resistance of every semiconductor wafer, and doing so would reduce operational efficiency. For these reasons, in actual practice, one of every predetermined number of semiconductor wafers is selected for measurement of the sheet resistance, which is regarded as being equivalent in effect to the measurement of the sheet resistance of every semiconductor wafer. This holds true with the foregoing four-probe scheme.
If some semiconductor wafers are removed from the manufacturing line for measurement of the sheet resistance, and the result of the measurement shows that the sheet resistance is not normal, all the semiconductor wafers including that semiconductor wafer back to the semiconductor wafer removed last time for the measurement of the sheet resistance must be checked to see whether the sheet resistance is normal or not.
In addition, to avoid further occurrence of abnormal sheet resistance and thereby bring the sheet resistance back to a normal value, the manufacturing line must be stopped to notify a CIM process management system and a thin film forming device of the abnormal value.
Therefore, in the foregoing four-probe scheme and non-contact-type sheet resistance measurement technique, no quick action can be taken when an abnormality occurs to the sheet resist
Conlin David G.
Cuneo Kamand
Daley, Jr. William J.
Nguyen Trung
LandOfFree
Sheet resisitance meter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sheet resisitance meter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sheet resisitance meter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3094015